I have watched the video for double knitting here and it seems very doable, however it didn't cover how you start a piece of work if you want it to be double knitting from start to finish or even how you'd transition from single to double knitting. If someone could explain:

1) How to cast on and begin double knitting from the beginning of a piece of work?

2) If you are starting a piece in single knitting and going to double, how do you go about doing the transition?